Interface Board

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fifty60

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USA
I am preparing to use this interface board http://sporlanonline.com/literature/100/ca/100-50-2.pdf.

The installation directions keep calling for a 30VA transformer. Is there any reason why a 30W switching power supply wouldn't work?

Are the instructions just using "transformer" as a generic term for power supply or is there a reason they want to use a transformer? I would normally call their tech support but they are out for the Holiday!
 

steve66

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Location
Illinois
Occupation
Engineer
I am preparing to use this interface board http://sporlanonline.com/literature/100/ca/100-50-2.pdf.

The installation directions keep calling for a 30VA transformer. Is there any reason why a 30W switching power supply wouldn't work?

Are the instructions just using "transformer" as a generic term for power supply or is there a reason they want to use a transformer? I would normally call their tech support but they are out for the Holiday!

It looks like the board is expecting a 24 volt AC supply. (To me, the 24 V+ and 24 V- labels on the terminals are a little confusing.) A switching supply would provide 24 volts DC. That may or may not work depending on the design of the boards AC to DC converter.

And then there is the note about not grounding one input from the power source. I'm not sure if your switch mode PS would be isolated from ground.
 

fifty60

Senior Member
Location
USA
The wiring connections says "power supplied may be 24 volts AC or DC." But the rest of the documents talks about the transformer which would be AC...

If I can use DC, I would float the output and not ground it so it could not interfere with the 4-20mA signal. There will not be anything else connected to the power supply that would force the output to be grounded either.
 
The installation directions keep calling for a 30VA transformer. Is there any reason why a 30W switching power supply wouldn't work?!

Beware that some things really don't like the output of a switching supply- depends on how much ripple and how fast it is (can it sneak by the 60Hz filter and mess with the electronics?). If a problem exists, sometimes just an HF bypass cap will solve it. I leave the actual engineering of this to someone else :).
 

gar

Senior Member
Location
Ann Arbor, Michigan
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EE
141231-1250 EST

My guess is that the board has a full wave bridge rectifier followed by a filter capacitor. The bridge rectifier is the reason that both power input leads need to be floated from ground (common). A bridge rectifier input means that you can feed from an isolated DC supply provided that no AC zero crossing signal is required. A 34 V DC supply probably should be used to replace a 24 V RMS sine wave.

I doubt that a DC output switching supply would present a problem. But what is wrong with a 24 V AC transformer? Long term reliability is probably greater with the 24 V AC transformer.

Run your own bench experiment.

.
 

rlundsrud

Senior Member
Location
chicago, il, USA
I do a lot of TC installations for Schneider and we always use 24v transformers as that is what Schneider specs. I personally would recommend using one as these TC boards can be pretty sensitive. Is it part of a Bacnet or some other RS-485 network or does it stand alone? I would be less concerned if it was a stand alone device, the serial networks can be a bit touchy.


*I should have looked at the product literature more closely. I see it doesn't have a serial connection, so you might be ok.
 
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gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
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rlundsrud:

RS-232, 422, and 485 don't have to be touchy. With dielectric isolation they can be very data reliable, even with very large common mode voltage between end points, or relative to earth.

.
 

rlundsrud

Senior Member
Location
chicago, il, USA
150101-0037 EST

rlundsrud:

RS-232, 422, and 485 don't have to be touchy. With dielectric isolation they can be very data reliable, even with very large common mode voltage between end points, or relative to earth.

.

My concern was that a switching supply might introduce noise into the com loop. It is something that isn't recommended with the Bacnet and Lonet com protocols, at least not by Schneider and automated logic
 
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